Interesting that people are admitting it, but this has probably been true for longer than I've been paying attention (about a decade) -- it's generally recognized that the first cut is deadwood, especially if the number is low (like the quoted myspace 5%).

An often overlooked silver lining to this is that a person under-performing in a position often has as much to do with the position as the performer. The person will probably go on to find a better, happier, more productive, or higher paying job elsewhere. Failure of a person in a role has as much to do with the management that put them in the position as the guy who ended up there, especially when the employer is in bulk-up mode.